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  Netty-05-异步模型
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      <h1 id="Netty-05-异步模型"><a href="#Netty-05-异步模型" class="headerlink" title="Netty-05-异步模型"></a>Netty-05-异步模型</h1><h2 id="前言"><a href="#前言" class="headerlink" title="前言"></a>前言</h2><ul>
<li>本文注重讲解Netty的<strong>异步模型</strong> 和 <strong>任务的队列</strong></li>
</ul>
<h2 id="1-任务队列"><a href="#1-任务队列" class="headerlink" title="1. 任务队列"></a>1. 任务队列</h2><p><img src="http://zhuuu-bucket.oss-cn-beijing.aliyuncs.com/img/20201024/085701217.png" alt="mark"></p>
<ul>
<li>任务队列由<code>NioEventLoop</code> 维护并且不断执行，当我们收到请求之后，在当前的 <code>channel</code> 中对应的 <code>pipeline</code>中的各个 <code>Hanlder</code>进行业务的处理和请求的过滤。</li>
<li>当某些业务需要消费大量事件的时候，我们可以将这些任务提交到由 <code>NioEventLoop</code> 维护的 <code>taskQueue</code> 或者 <code>ScheduleTaskQueue</code>中， 让当前的 NioEventLoop 线程在空闲的时候去执行这些任务。</li>
<li><strong>下面将介绍提交任务的三种方式:</strong></li>
</ul>
<a id="more"></a>



<h3 id="1-1-用户程序自定义的普通任务"><a href="#1-1-用户程序自定义的普通任务" class="headerlink" title="1.1 用户程序自定义的普通任务"></a>1.1 用户程序自定义的普通任务</h3><ul>
<li>该方式会将任务提交到<code>taskQueue</code>队列中。提交到该队列中的任务会按照提交顺序依次执行。</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">channelHandlerContext.channel().eventLoop().execute(<span class="keyword">new</span> Runnable()&#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">run</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="comment">//...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;);</span><br></pre></td></tr></table></figure>





<h3 id="1-2-用户自定的定时任务"><a href="#1-2-用户自定的定时任务" class="headerlink" title="1.2 用户自定的定时任务"></a>1.2 用户自定的定时任务</h3><ul>
<li>该方式会将任务提交到<code>scheduleTaskQueue</code>定时任务队列中。该队列是底层是优先队列<code>PriorityQueue</code>实现的，固该队列中的任务会按照时间的先后顺序定时执行。</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">channelHandlerContext.channel().eventLoop().schedule(<span class="keyword">new</span> Runnable() &#123;</span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">run</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="comment">//...</span></span><br><span class="line">    &#125;</span><br><span class="line">&#125;, <span class="number">60</span>, TimeUnit.SECONDS);</span><br></pre></td></tr></table></figure>



<h3 id="1-3-为其他的-EventLoop-线程对应的-Channel添加任务"><a href="#1-3-为其他的-EventLoop-线程对应的-Channel添加任务" class="headerlink" title="1.3 为其他的 EventLoop 线程对应的 Channel添加任务"></a>1.3 为其他的 EventLoop 线程对应的 Channel添加任务</h3><ul>
<li><strong>可以在<code>ChannelInitializer</code>中，将刚创建的各个<code>Channel</code>以及对应的标识加入到统一的集合中去</strong></li>
<li>然后可以根据表示获取 Channel 对应的 NioEventLoop,然后就可以调用<code>execute()</code>或者<code>schedule()</code>方法。</li>
</ul>
<h2 id="2-异步模型"><a href="#2-异步模型" class="headerlink" title="2. 异步模型"></a>2. 异步模型</h2><h3 id="2-1-异步的概念"><a href="#2-1-异步的概念" class="headerlink" title="2.1 异步的概念"></a>2.1 异步的概念</h3><ul>
<li>异步的概念和同步是相对的，当一个异步过程调用发出后，调用者不能立即的得到结果。实际处理这个调用的组件在完成后，<strong>通过状态，通知和回调来通知调用者</strong></li>
<li><code>Netty</code> 中的 <code>I/O</code> 操作是异步的，包括 <code>Bind</code>、<code>Write</code>、<code>Connect</code> 等操作会简单的返回一个 <code>ChannelFuture</code>。</li>
<li>调用者并不能立即获得结果，而是通过 <code>Future-Listener</code> 机制，用户可以方便的主动获取或者通过通知机构获取IO 的操作结果。</li>
</ul>
<p><strong>机制描述</strong></p>
<ul>
<li><code>Netty</code> 的异步模型是建立在 <code>future</code> 和 <code>callback</code> 的之上的。<code>callback</code> 就是回调。重点说 <code>Future</code>，它的核心思想是：假设一个方法 <code>fun</code>，计算过程可能非常耗时，等待 <code>fun</code>返回显然不合适。那么可以在调用 <code>fun</code> 的时候，立马返回一个 <code>Future</code>，后续可以通过 <code>Future</code>去监控方法 <code>fun</code> 的处理过程(即 ： <code>Future-Listener</code> 机制)</li>
</ul>
<p><strong>关于 Future 的说明</strong></p>
<ul>
<li>表示异步的执行结果, 可以通过它提供的方法来检测执行是否完成，比如检索计算等等.</li>
<li><code>ChannelFuture</code> 是一个接口 ： <code>public interface ChannelFuture extends Future&lt;Void&gt;</code>。我们可以添加监听器，当监听的事件发生时，就会通知到监听器</li>
</ul>
<p><strong>工作原理示意图</strong></p>
<p><img src="http://zhuuu-bucket.oss-cn-beijing.aliyuncs.com/img/20201028/215425984.png" alt="mark"></p>
<p><img src="http://zhuuu-bucket.oss-cn-beijing.aliyuncs.com/img/20201028/215442367.png" alt="mark"></p>
<ul>
<li>在使用 <code>Netty</code> 进行编程时，拦截操作和转换出入站数据只需要您提供 <code>callback</code> 或利用<code>future</code> 即可。这使得链式操作简单、高效, 并有利于编写可重用的、通用的代码。</li>
<li><code>Netty</code> 框架的目标就是让你的业务逻辑从网络基础应用编码中分离出来、解脱出来</li>
</ul>
<h3 id="2-2-Future-Listener-机制"><a href="#2-2-Future-Listener-机制" class="headerlink" title="2.2 Future-Listener 机制"></a>2.2 Future-Listener 机制</h3><ul>
<li>当 <code>Future</code> 对象刚刚创建时，处于非完成状态，调用者可以通过返回的 <code>ChannelFuture</code> 来获取操作执行的状态，注册监听函数来执行完成后的操作。</li>
</ul>
<p><strong>常用方法如下：</strong></p>
<table>
<thead>
<tr>
<th>方法名称</th>
<th>方法作用</th>
</tr>
</thead>
<tbody><tr>
<td>isDone()</td>
<td>判断当前操作是否完成</td>
</tr>
<tr>
<td>isSuccess()</td>
<td>判断已完成的当前操作是否成功</td>
</tr>
<tr>
<td>getCause()</td>
<td>获取已完成当前操作失败的原因</td>
</tr>
<tr>
<td>isCancelled()</td>
<td>判断已完成的当前操作是否被取消</td>
</tr>
<tr>
<td>addListener()</td>
<td>注册监听器，当前操作（Future）已完成，将会通知指定的监听器</td>
</tr>
</tbody></table>
<p><strong>举例说明</strong></p>
<ul>
<li>绑定端口操作时异步操作，当绑定操作处理完，将会调用相应的监听器处理逻辑。</li>
</ul>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">serverBootstrap.bind(port).addListener(future -&gt; &#123;</span><br><span class="line">       <span class="keyword">if</span>(future.isSuccess()) &#123;</span><br><span class="line">           System.out.println(newDate() + <span class="string">": 端口["</span>+ port + <span class="string">"]绑定成功!"</span>);</span><br><span class="line">       &#125; <span class="keyword">else</span>&#123;</span><br><span class="line">           System.err.println(<span class="string">"端口["</span>+ port + <span class="string">"]绑定失败!"</span>);</span><br><span class="line">       &#125;</span><br><span class="line">   &#125;);</span><br></pre></td></tr></table></figure>



<h3 id="2-3-HTTP-实战入门"><a href="#2-3-HTTP-实战入门" class="headerlink" title="2.3 HTTP 实战入门"></a>2.3 HTTP 实战入门</h3><p><strong>目标 ：  浏览器访问<code>Netty</code>服务器后，返回<code>HelloWorld</code></strong></p>
<ol>
<li><strong>启动器</strong></li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> io.netty.bootstrap.ServerBootstrap;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.ChannelFuture;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.nio.NioEventLoopGroup;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.socket.nio.NioServerSocketChannel;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">TestServer</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line">        NioEventLoopGroup bossGroup = <span class="keyword">new</span> NioEventLoopGroup(<span class="number">1</span>);</span><br><span class="line">        NioEventLoopGroup workerGroup = <span class="keyword">new</span> NioEventLoopGroup();</span><br><span class="line"></span><br><span class="line">        <span class="keyword">try</span>&#123;</span><br><span class="line">            ServerBootstrap serverBootstrap = <span class="keyword">new</span> ServerBootstrap();</span><br><span class="line">            serverBootstrap.group(bossGroup,workerGroup)</span><br><span class="line">                    .channel(NioServerSocketChannel<span class="class">.<span class="keyword">class</span>)</span></span><br><span class="line"><span class="class">                    .<span class="title">childHandler</span>(<span class="title">new</span> <span class="title">TestServerInitializer</span>())</span>;</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 绑定端口号操作</span></span><br><span class="line">            ChannelFuture channelFuture = serverBootstrap.bind(<span class="number">8080</span>).sync();</span><br><span class="line">            channelFuture.channel().closeFuture().sync();</span><br><span class="line">        &#125; <span class="keyword">catch</span> (InterruptedException e) &#123;</span><br><span class="line">            e.printStackTrace();</span><br><span class="line">        &#125; <span class="keyword">finally</span> &#123;</span><br><span class="line">            <span class="comment">// 关闭线程池</span></span><br><span class="line">            bossGroup.shutdownGracefully();</span><br><span class="line">            workerGroup.shutdownGracefully();</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>





<ol start="2">
<li><p><strong>自定义ChannelInitializer</strong></p>
<p><strong>用于给<code>Channel</code>对应的<code>pipeline</code>添加<code>handler</code></strong>。该<code>ChannelInitializer</code>中的代码在<code>SocketChannel</code>被创建时都会执行</p>
</li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> io.netty.channel.Channel;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.ChannelInitializer;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.ChannelPipeline;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.socket.SocketChannel;</span><br><span class="line"><span class="keyword">import</span> io.netty.handler.codec.http.HttpServerCodec;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">TestServerInitializer</span> <span class="keyword">extends</span> <span class="title">ChannelInitializer</span>&lt;<span class="title">SocketChannel</span>&gt; </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">initChannel</span><span class="params">(SocketChannel channel)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 向管道加入处理器</span></span><br><span class="line">        <span class="comment">// 首先得到管道</span></span><br><span class="line">        ChannelPipeline pipeline = channel.pipeline();</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 1. 加入一个netty提供的HttpServerCodec</span></span><br><span class="line">        <span class="comment">// netty自带的http编码解码器</span></span><br><span class="line">        pipeline.addLast(<span class="string">"MyHttpServerCodec"</span>,<span class="keyword">new</span> HttpServerCodec());</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 2. 增加自定义handler</span></span><br><span class="line">        pipeline.addLast(<span class="string">"MyTestHttpServerHandler"</span>,<span class="keyword">new</span> TestHttpServerHandler());</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>



<ol start="3">
<li><strong>自定义Handler</strong></li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> io.netty.buffer.ByteBuf;</span><br><span class="line"><span class="keyword">import</span> io.netty.buffer.Unpooled;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.ChannelHandlerContext;</span><br><span class="line"><span class="keyword">import</span> io.netty.channel.SimpleChannelInboundHandler;</span><br><span class="line"><span class="keyword">import</span> io.netty.handler.codec.http.*;</span><br><span class="line"><span class="keyword">import</span> io.netty.util.CharsetUtil;</span><br><span class="line"></span><br><span class="line"><span class="keyword">import</span> java.net.URI;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">TestHttpServerHandler</span> <span class="keyword">extends</span> <span class="title">SimpleChannelInboundHandler</span>&lt;<span class="title">HttpObject</span>&gt; </span>&#123;</span><br><span class="line">    <span class="comment">/**</span></span><br><span class="line"><span class="comment">     * 读取客户端的数据</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> channelHandlerContext</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@param</span> httpObject 客户端和服务端互相通讯所使用的对象</span></span><br><span class="line"><span class="comment">     * <span class="doctag">@throws</span> Exception</span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">void</span> <span class="title">channelRead0</span><span class="params">(ChannelHandlerContext channelHandlerContext, HttpObject httpObject)</span> <span class="keyword">throws</span> Exception </span>&#123;</span><br><span class="line">        <span class="comment">// 判断msg 是不是 HttpRequest请求</span></span><br><span class="line">        <span class="keyword">if</span>(httpObject <span class="keyword">instanceof</span> HttpRequest)&#123;</span><br><span class="line">            System.out.println(<span class="string">"msg 类型 = "</span> + httpObject.getClass());</span><br><span class="line">            System.out.println(<span class="string">"客户端地址："</span> + channelHandlerContext.channel().remoteAddress());</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 获取http请求</span></span><br><span class="line">            HttpRequest request = (HttpRequest) httpObject;</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 从http请求中获取uri</span></span><br><span class="line">            URI uri = <span class="keyword">new</span> URI(request.uri());</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 过滤http中的请求</span></span><br><span class="line">            <span class="keyword">if</span> (<span class="string">"/favicon.ico"</span>.equals(uri.getPath()))&#123;</span><br><span class="line">                System.out.println(<span class="string">"请求了 favicon.ico，不做响应"</span>);</span><br><span class="line">            &#125;</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 回复信息给浏览器[http协议]</span></span><br><span class="line">            ByteBuf content = Unpooled.copiedBuffer(<span class="string">"helloWorld"</span>, CharsetUtil.UTF_8);</span><br><span class="line">            <span class="comment">// 构造一个http响应回复给浏览器</span></span><br><span class="line">            DefaultFullHttpResponse response = <span class="keyword">new</span> DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK, content);</span><br><span class="line">            response.headers().set(HttpHeaderNames.CONTENT_TYPE,<span class="string">"text/plain"</span>);</span><br><span class="line">            response.headers().set(HttpHeaderNames.CONTENT_LENGTH,content.readableBytes());</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 将构建好的response返回给客户端</span></span><br><span class="line">            channelHandlerContext.writeAndFlush(response);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>


      
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